Manhattan Project security and secrecy regime

The Manhattan Project security and secrecy regime was the system of fences, access controls, information restrictions, internal rules, and surveillance surrounding the wartime bomb project. It protected a military undertaking whose scientists needed to exchange difficult technical knowledge, but also placed them under Army authority and scrutiny. In Los Alamos, that tension was not abstract: it shaped who could enter a home or laboratory, what could be said in a meeting, and whether a paper left on a desk overnight could become an infraction.

A guarded workplace

At Los Alamos, security had both an external and an internal architecture. Armed military police were stationed outside J. Robert Oppenheimer’s house on Bathtub Row, inspecting every pass, including Katherine (Kitty) Oppenheimer’s, before permitting entry. Kitty sometimes forgot her pass and protested when she was refused reentry; on occasion, she also enlisted the MPs to watch Peter. When the sergeant discovered the improvised babysitting arrangement, he withdrew the detail. The episode captures how military controls reached beyond the laboratory into family life, even as residents found ways to make the apparatus serve ordinary needs.

Inside the site, Oppenheimer had agreed with Leslie Groves to appoint a three-person committee for internal security. His assistants David Hawkins and John Manley, along with chemist Joe Kennedy, were responsible for security within the laboratory’s T-Section. That area sat behind a second barbed-wire fence, beyond the reach of MPs and soldiers. Security therefore was not simply an Army presence imposed from outside: civilian scientists were also assigned to police the laboratory’s daily routines.

Some of those routines were deliberately mundane. Scientists were expected to lock file cabinets when leaving their offices. Anyone found to have left a secret paper on a desk overnight had to patrol the laboratory the following night and try to catch another offender. When Hawkins told Emilio Segrè that a paper left out required him to take his turn, Segrè answered that the document was wrong and would only confuse the enemy. The exchange makes the regulations tangible: a breach prompted not merely reprimand but a small, compulsory turn at enforcing the system.

Compartmentalization and scientific exchange

The regime restricted information at the same time that the project required scientists to understand work beyond their immediate specialties. During the summer seminar of 1942, the physicists met in an attic room at LeConte Hall, above Oppenheimer’s Berkeley office. French doors opened onto a balcony covered with thick wire netting; Oppenheimer alone held the key. When sunlight projected the netting’s shadow across the papers on the table, Joe Weinberg recalled that the scientists seemed, for a moment, to be inside a symbolic cage. The image joined an actual security barrier to the intellectual atmosphere of work conducted under restriction.

At Los Alamos, Oppenheimer nevertheless supported structured opportunities for broader discussion. When Hans Bethe proposed a weekly, open-ended colloquium, Oppenheimer agreed, despite Groves’s initial attempt to stop it. Oppenheimer argued that a leisurely, thorough discussion could help scientists overcome the effects of information being “highly compartmentalized.” The first meeting, held on April 15, 1943, in an empty schoolboys’ library, brought together no more than forty scientists. Oppenheimer introduced Robert Serber, who summarized the project’s work and described the proposed weapon. When Serber used the word “bomb,” Oppenheimer sent John Manley to suggest the more neutral “gadget.” The meeting thus joined technical disclosure to the vocabulary and precautions of secrecy: knowledge was shared within a defined group, but even its naming was managed.

This tension reflected a wider contrast in scientific practice. The enormous, resource-intensive machines associated with Ernest Lawrence and the Berkeley Radiation Laboratory belonged to the rise of “big science,” increasingly connected to corporate resources and military work. Oppenheimer’s theoretical physics had been associated with “small” science. At Los Alamos, the scale and purpose of the enterprise made collaboration essential, while security sought to limit the circulation on which collaboration relied. The controls were not incidental to the work; they helped shape its organization.

Surveillance beyond the fence

The formal rules were accompanied by pervasive monitoring. Oppenheimer complained that he could not speak to his own brother and that telephone calls were being monitored. Robert Wilson initially regarded his complaints as “somewhat paranoiac,” but later learned that Oppenheimer had indeed been under near-total surveillance. Mail was monitored, the home telephone was watched, and his office was wiretapped. Andrew Walker, assigned as his driver and bodyguard, was also a Counter-Intelligence Corps agent reporting to Colonel Boris Pash.

The surveillance extended beyond Oppenheimer himself. Before Los Alamos opened in March 1943, the Army instructed J. Edgar Hoover to suspend FBI surveillance of Oppenheimer; Hoover complied beginning March 22, while directing agents in San Francisco to continue watching people who might have been associated with him in the Communist Party. The Army, meanwhile, had arranged full-time technical and physical surveillance of Oppenheimer, and undercover officers had been assigned before he arrived. In later years, while he remained employed by the government, variations of the same scrutiny continued: associates and past political connections were repeatedly investigated, and he was repeatedly made to understand that he himself was suspected of Communist Party membership.

Oppenheimer adapted to this pressure as well as objecting to it. The once-casual professor began carefully pinning classified memoranda inside his hip pocket so he would not lose them. He gave security officers time and complied with nearly all their requests. Yet the strain and the investigations into his past led him, in the summer of 1943, to tell Robert Bacher that he was thinking of quitting. Bacher’s reply was that no one else could do the job. Oppenheimer stayed, but the episode shows the personal cost of a system that treated its scientific director as both indispensable and suspect.

Friction, resistance, and the limits of secrecy

The regime provoked irritation, humor, and conflict. Richard Feynman frustrated censors who suspected that letters from his wife, Arline, were written in code; he explained that they were playing a code-breaking game and that he did not possess the key. He also opened combination locks on classified file cabinets during a nighttime safecracking spree. After noticing a hole in the perimeter fence, he repeatedly exited through the main gate, crawled through the hole, and then walked out through the gate again. He was nearly arrested, and the episodes became part of Los Alamos lore. His stunts exposed the gap between the rules’ formal authority and the practical ingenuity of the people expected to live under them.

Oppenheimer’s own resistance was less theatrical but more consequential. He tried to protect colleagues from security officers whom he feared would remove too many people from the project, and he opposed restrictions that blocked useful scientific exchange. The Army’s relations with the scientists and their families remained unstable; Groves privately called the civilians “the children,” while insisting that living conditions and family problems should not distract them from their work. Oppenheimer could work with Groves, but found many counterintelligence officers obtuse and offensive. At a meeting disrupted by a captain’s complaint that a scientist had sat on his desk, Oppenheimer answered that in the laboratory anyone could sit on anybody’s desk. The rebuke asserted a local scientific community’s norms against an officer’s insistence on rank and decorum.

The contrast with Niels Bohr’s postwar argument clarifies what wartime secrecy left unresolved. Bohr believed that international control of atomic energy required an “open world,” with international inspectors able to access military and industrial complexes and obtain information about scientific discoveries. He and Oppenheimer held that secrecy could not provide lasting security if nations feared that rivals were stockpiling weapons. In the wartime project, by contrast, knowledge was enclosed behind fences, restricted meetings, and monitored communication. The regime enabled work on a weapon under wartime conditions, but its practices also dramatized the conflict between military control and open scientific inquiry—a conflict that persisted after the laboratory’s gates ceased to define its boundaries.